Selection of Butterfly Valve Caliber
Caliber of a butterfly valve is mainly determined on flow, media and flow rate. Generally, the flow rate of the liquid is not more than 5m / s, maximum 7-8m / s. Typically, the water flow rate is 2-3m / s, low pressure gas flow rate is recommended 2-10m / s, medium pressure gas flow rate is recommended 10-20m / s. For steam flow rate, low pressure steam flow rate is recommended 20-40m / s, medium-pressure steam flow rate is 40 -60m / s while high-pressure steam flow rate is 60-80m / s.
Of course, sometimes, in order to reduce the pressure loss, people will select a butterfly valve with larger caliber, so that the flow rate will be slower. But if the valve worked in a small flow, you can not do so.
The liquid to flow through an absolute low pressure zone and have rapid evaporation and recondensation phenomena in a very short period of time is called cavitation. Because the gas can not change its state under a low pressure, so this phenomenon will not appear in the airstream. When the fluid flows into the high pressure zone, steam bubbles will suddenly condense, collapse or get together stormily, and the flow rate could reach 110m / s and 50Mpa, causing an impact damage to the wall. Therefore, to avoid this kind of cavitation, people should take these following measures.
1 Control the flow rate to avoid such a low pressure.
2 Bring the atmosphere into pressure zone.
When the valve pressure is less than 1.5Mpa and cause cavitation phenomenon, however, it will not damage the material seriously, so you don't have to take special measures.